1. Field of the Invention
A toroidal type continuously variable transmission according to the present invention can be used, for example, as a speed change unit of a transmission of a motor vehicle or transmissions of various industrial machines.
2. Related Background Art
A toroidal type continuously variable transmission schematically shown in FIGS. 7 and 8 has been investigated for use as a transmission of a motor vehicle. For example, as disclosed in Japanese Utility Model Laid-Open Application No. 62-71465, in such a toroidal type continuously variable transmission, an, input side disk 2 is supported in coaxial relationship with an input shaft 1 and an output side disk 4 is secured to an end of an output shaft 3 disposed in coaxial relationship with the input shaft 1. Within a casing containing the torodial type continuously variable transmission, there are provided trunnions 6 rockable around pivot shafts 5 transverse to the input shaft 1 and the output shaft 3.
Each trunnion 6 is provided at opposite end surfaces with the pivot shafts 5 in coaxial relationship with each other. Further, central portions of the trunnions 6 support proximal ends of displacement shafts 7 so that inclination angles of the displacement shafts 7 can be adjusted by rocking or swinging the trunnions 6 around the pivot shafts 5. Power rollers 8 are rotatably supported around the displacement shafts 7 supported by the trunnions 6. The power rollers 8 are interposed between opposed inner surfaces 2a and 4a of the input side disk 2 and the output side disk 4. The inner surfaces 2a, 4a have concave surfaces obtained by rotating arcs having centers on the pivot shafts 5. Peripheral surfaces 8a of the power rollers 8 having spherical convex shapes abut against the inner surfaces 2a, 4a. 
A pressing device 9 of loading cam type is disposed between the input shaft 1 and the input side disk 2 so that the input side disk 2 can be urged elastically toward the output side disk 4 by the pressing device 10. The pressing device 9 comprises a loading cam (cam plate) 10 rotated together with the input shaft 1, and a plurality (for example, four) of rollers 12 rotatably held by a holder 11. One side surface (right side surface in FIGS. 7 and 8) of the loading cam 10 is constituted as a cam surface 13 having unevenness or undulation extending along a circumferential direction, and an outer surface (left side surface in FIGS. 7 and 8) of the input side disk 2 has a similar cam surface 14. The plurality of rollers 12 are rotatably supported for rotation around axes extending radially with respect to the center line of the input shaft 1.
In use of the toroidal type continuously variable transmission having the above-mentioned construction, when the loading cam 10 is rotated as the input shaft 1 is rotated, the plurality of rollers 12 are urged against the cam surface 14 formed on the outer surface of the input side disk 2 by the cam surface 13. As a result, the input side disk 2 is urged against the plurality of power rollers 8, and, at the same time, due to the frictional engagement between the cam surfaces 13, 14 and the plurality of rollers 12, the input side disk 2 is rotated. Rotation of the input side disk 2 is transmitted to the output side disk 4 through the plurality of power rollers 8, thereby rotating the output shaft 3 secured to the output side disk 4.
In a case where a rotational speed ratio (speed change ratio) between the input shaft 1 and the output shaft 3 is changed, when deceleration is effected between the input shaft 1 and the output shaft 3, the trunnions 6 are rocked or swung around the pivot shafts 5 in predetermined directions, thereby inclining the displacement shafts 7 so that the peripheral surfaces 8a of the power rollers 8 abut against a portion of the inner surface 2a of the input side disk 2 near the center and a portion of the inner surface 4a of the output side disk 4 near its outer periphery, respectively, as shown in FIG. 7. On the other hand, when acceleration is effected, the trunnions 6 are rocked around the pivot shafts 5 in opposite directions, thereby inclining the displacement shafts 7 so that the peripheral surfaces 8a of the power rollers 8 abut against a portion of the inner surface 2a of the input side disk 2 near its outer periphery and a portion of the inner surface 4a of the output side disk 4 near the center, respectively, as shown in FIG. 8. If the inclination angles of the displacement shafts 7 are selected to an intermediate value between FIG. 7 and FIG. 8, an intermediate speed change ratio can be obtained.
FIGS. 9 and 10 show an example of a toroidal type continuously variable transmission, described in Japanese Utility Model Application Laid-Open No. 1-173552. An input side disk 2 and an output side disk 4 are rotatably supported around a cylindrical input shaft 15 via needle bearings 16, respectively. Through holes 17 having circular cross-section are formed in central portions of the input side disk 2 and the output side disk 4 so that they pass through inner and outer surfaces of the disks 2, 4 axially (in a left-and-right direction in FIG. 9). The needle bearings 16 are disposed between inner peripheral surfaces of the through holes 17 and an outer peripheral surfaces of an intermediate portion of the input shaft 15. Further, locking grooves 18 formed in inner peripheral surfaces of the through holes 17 near inner surfaces receive stop rings 19 to prevent the needle bearings 16 from dislodging from the through holes 17 toward the inner surfaces 2a, 4a of the disks 2, 4. A loading cam 10 is spline-connected to an end (left end in FIG. 9) of the input shaft 15 so that the loading cam is prevented from shifting away from the input side disk 2 by a flange 20. The loading cam 10 and rollers 12 constitute a pressing device 9 for rotating the input side disk 2 while urging the input side disk toward the output side disk 4 in response to rotation of the input shaft 15. An output gear 21 is coupled to the output side disk 4 via keys 22 so that the output side disk 4 and the output gear 21 are rotated in a synchronous manner.
The ends of a pair of trunnions 6 are supported by a pair of support plates 23 for rocking movement and axial displacement movement (in a front-and-rear direction in FIG. 9 and left-and-right direction in FIG. 10). Circular holes 24 formed in intermediate portions of the trunnions 6 support displacement shafts 7. The displacement shafts 7 have support shaft portions 25 and pivot shaft portions 26 which are parallel to each other and are eccentric from each other. The support shaft portions 25 are rotatably supported within the circular holes 24 via radial needle bearings 27. Further, power rollers 8 are rotatably supported around the pivot shaft portions 26 via other radial needle bearings 28.
The pair of displacement shafts 7 are disposed at positions diametrically opposed with respect to the input shaft 15. Further, directions along which the pivot shaft portions 26 of the displacement shafts 7 are eccentric with respect to the support shaft portions 25 are the-same with respect to the rotational directions of the input side and output side disk 2, 4 (opposite directions in FIG. 10). Further, the eccentric directions are substantially perpendicular to the extending direction of the input shaft 15. Accordingly, the power rollers 8 are supported for slight displacement along the extending direction of the input shaft 15. As a result, due to elastic deformation of structural members caused by great load acting on the members in the rotational force transmitting condition, even when the power rollers 8 have tendency for displacing toward the axial direction (left-and-right direction in FIG. 9 and front-and-rear direction in FIG. 10) of the input shaft 15, the displacement can be absorbed without applying excessive force to the structural elements.
Further, between the outer surfaces of the power rollers 8 and the inner surfaces of the intermediate portions of the trunnions 6, there are disposed thrust ball bearings 29 and thrust needle bearings 30 in order from the outer surfaces of the power rollers 8. The thrust ball bearings 29 permit rotations of the power rollers 8 while supporting thrust load acting on the power rollers 8. The thrust needle bearings 30 permit the pivot shaft portions 26 and outer races 31 constituting parts of the thrust ball bearings 29 to rock around the support shaft portions 25 while supporting thrust load acting on the outer races 31 from the power rollers 8.
Further, drive rods 32 are connected to respective ends (left ends in FIG. 10) of the trunnions 6, and drive pistons 33 are secured to outer peripheral surfaces of intermediate portions of the drive rods 32. The drive pistons 33 are mounted within drive cylinders 34 in an oil tight fashion.
In the case of the toroidal type continuously variable transmission having the above-mentioned construction, the rotation of the input shaft 15 is transmitted to the input side disk 2 through the pressing device 9. The rotation of the input side disk 2 is transmitted to the output side disk 4 through the pair of power rollers 8, and the rotation of the output side disk 4 is picked up by the output gear 21. When the rotational speed ratio between the input shaft 15 and the output gear 21 is changed, the pair of drive pistons 33 are displaced in opposite directions. In response to the displacement of the drive pistons 33, the pair of trunnions 6 are displaced in opposite directions, with the result that, for example, the lower (in FIG. 10) power roller 8 is displaced to the right in FIG. 10 and the upper (in FIG. 10) power roller 8 is displaced to the left in FIG. 10. As a result, directions of tangential forces acting on contact areas between the peripheral surfaces 8a of the power rollers 8 and the inner surfaces 2a, 4a of the input and output side disks 2, 4 are changed. In response to the change in directions of forces, the trunnions 6 are rocked in opposite directions around the pivot shafts 5 rotatably supported by the support plates 23. As a result, as shown in FIGS. 7 and 8, the contact areas between the peripheral surfaces 8a of the power rollers 8 and the inner surfaces 2a, 4a are changed, thereby changing the rotational speed ratio between the input shaft 15 and the output gear 21.
Incidentally, when the rotational force is transmitted between the input shaft 15 and the output gear 21 in this way, in response to the elastic deformation of the structural members, the power rollers 8 are displaced in the axial direction of the input shaft 15 and the displacement shafts 7 rotatably supporting the power rollers 8 are slightly rotated around the support shaft portions 25. As a result of such rotation, outer surfaces of the outer races 31 of the thrust ball bearings 29 and inner surfaces of the trunnions 6 are displaced relative to each other. Since the thrust needle bearings 30 are disposed between such outer surfaces and inner surfaces, a force required for effecting such relative displacement is small. Accordingly, a force for changing the inclination angles of the displacement shafts 7 becomes small.
Further, as shown in FIGS. 11 and 12, there has been proposed an arrangement of so-called double cavity type in which two input side disks 2A, 2B corresponding to first and second outer disks and two output side disks 4 corresponding to first and second inner disks are provided around an input shaft 15a and the two input side disks 2A, 2B and the two output side disks 4 are arranged in parallel with respect to a power transmitting direction. In the arrangement shown in FIGS. 11 and 12, an output gear 21a is supported around an intermediate portion of the input shaft 15a for rotation with respect to the input shaft 15a and the output side disks 4 are spline-connected to both ends of a cylindrical sleeve 45 provided on the center of the output gear 21a. Needle bearings 16 are provided between inner peripheral surfaces of through holes 17 formed in the output side disks 4 and an outer peripheral surface of the input shaft 15a so that the output side disks 4 are supported around the input shaft 15a for rotation and axial displacement movement with respect to the input shaft 15a. Further, the input side disks 2A, 2B are supported on both ends of the input shaft 15a for rotation together with the input shaft 15a. The input shaft 15a is rotatingly driven by a drive shaft 35 through a pressing device 9 of loading cam type. Incidentally, a radial bearing 36 such as a sliding bearing or a needle bearing is disposed between an outer peripheral surface of a leading end portion (right end portion in FIGS. 11 and 12) of-the drive shaft 35 and an inner peripheral surface of a proximal end (left end in FIGS. 11 and 12) of the input shaft 15a. Accordingly, the drive shaft 35 and the input shaft 15a are arranged in a coaxial relationship and are assembled for slight displacement in a rotational direction.
A back surface (right surface in FIGS. 11 and 12) of one (right one in FIGS. 11 and 12) of the input side disks 2A abuts against a loading nut 37 via a cone-shaped leaf spring 38 having great elasticity, thereby substantially preventing axial (left-and-right direction in FIGS. 11 and 12) displacement of the input side disk relative to the input shaft 15a. On the other hand, the input side disk 2B opposed to the loading cam 10 is supported on the input shaft 15a via a ball spline 39 for axial displacement movement. A cone-shaped leaf spring 41 is disposed between an outer surface (left surface in FIGS. 11 and 12) of the input side disk 2B and a locking stepped portion formed on the outer peripheral surface of the intermediate portion of the input shaft 15a. The cone-shaped leaf spring 41 has elasticity smaller than that of the cone-shaped leaf spring 38 and serves to apply pre-pressure to contact areas between the inner surfaces 2a, 4a of the disks 2A, 2B, 4 and the peripheral surfaces 8a of the power rollers 8.
Further, the output gear 21a is rotatably supported by a partition wall 42 within the housing via a pair of ball bearings 43 of angular type while preventing axial displacement of the output gear. Incidentally, the reason why the toroidal type continuously variable transmission of double cavity type shown in FIGS. 11 and 12 supports one or both of the input side disks 2A, 2B opposed to the loading cam 10 on the input shaft 15a for axial displacement movement via the ball splines 39 is that the both disks 2A, 2B can be displaced in the axial direction with respect to the input shaft 15a in response to elastic deformation of structural members caused by the operation of the pressing device 9 while synchronizing the rotations of both disks 2A, 2B.
When the above-mentioned toroidal type continuously variable transmission of double cavity type is operated, the rotation of the drive shaft 35 is transmitted to the (left in FIG. 11) input side disk 2B through the pressing device 9 and then the rotation is transmitted to the other input side disk 2A through the input shaft 15a, with the result that, both input side disks 2A, 2B are rotated synchronously. The rotation of the input side disks 2A, 2B is transmitted to the pair of output side disks 4 through the plurality (two pairs in the illustrated example) of power rollers 8. As a result, the sleeve 45 having both ends spline-connected to the is output side disks 4 is rotated, so that the output gear 21a secured to the outer peripheral surface of the intermediate portion of the sleeve 45 is also rotated. In this way, in the toroidal type continuously variable transmission of double cavity type, since the transmission of rotation from the drive shaft 35 to the output gear 21a is effected by two parallel systems, great torque can be transmitted. Further, by changing the inclination angles of the power rollers 8 disposed between the disks 2A, 2B, 4 in a synchronous manner, the speed change ratio between the input side disks 2A, 2B and the output side disks 4 can be changed.
In case of the conventional arrangement shown in FIGS. 11 and 12, since the pair of output side disks 4 are spline-connected to both ends of the sleeve 45 to which the output gear 21a is secured, thickness of both ends of the sleeve 45 becomes inevitably smaller. Thus, torsional rigidity of the ends is reduced, with the result that it is difficult to transmit great torque between the output side disks 4 and the sleeve 45. Increase in thickness of the sleeve 45 is not preferable because it will be difficult to make the toroidal type continuously variable transmission compact and lightweight.
The present invention is made in consideration of the above-mentioned circumstances.
As is in conventional toroidal type continuously variable transmissions of double cavity type, for example, as shown in FIGS. 11 and 12, a toroidal type continuously variable transmission according to the present invention comprises first and second outer disks supported in coaxial relationship with each other and capable of being rotated synchronously in such an arrangement that inner surfaces of the disks are opposed to each other, a first inner disk supported in coaxial relationship with the first and second outer disks and capable of being rotated independently from the first and second outer disks and having an inner surface opposed to the inner surface of the first outer disk, a second inner disk supported in coaxial relationship with the first inner disk and capable of being rotated synchronously with the first inner disk and having an inner surface opposed to the inner surface of the second outer disk, a plurality of first pivot shafts disposed between the first outer disk and the first inner disk at positions where the pivot shafts do not intersect with a central axis of these discs but extend along directions perpendicular to the central axis, a plurality of first trunnions rockable around the first pivot shafts, first displacement shafts protruded from inner surfaces of the first trunnions, a plurality of first power rollers rotatable supported around the first displacement shafts and interposed between the inner surface of the first outer disk and the inner surface of the first inner disk, a plurality of second pivot shafts disposed between the second outer disk and the second inner disk at positions where the pivot shafts do not intersect with a central axis of these discs but extend along directions perpendicular to the central axis, a plurality of second trunnions rockable around the second pivot shafts, second displacement shafts protruded from inner surfaces of the second trunnions, and a plurality of second power rollers rotatably supported around the second displacement shafts and interposed between the inner surface of the second outer disk and the inner surface of the second inner disk; and the first and second inner disks are supported on both end portions of a cylindrical sleeve for rotation in synchronous manner with the sleeve.
Particularly in the toroidal type continuously variable transmission according to the present invention, concave portions or convex portions are formed on the opposed outer surfaces of the first and second inner disks, and convex portions or concave portions are formed on edge portions of the axial ends of the sleeve. And, by engaging the concave portions or convex portions formed on the opposed outer surfaces of the first and second inner disks with the convex portions or concave portions formed on the edge portions of the axial ends of the sleeve, synchronous rotations of the first and second inner disks and transmission of a rotational force between the first and second inner disks and the sleeve can be achieved.
The function of the toroidal type continuously variable transmission of the present invention having the above-mentioned arrangements for transmitting the rotational force from the first and second outer disks to the first and second inner disks through the two systems and the function for changing the speed change ratio between the first and second outer disks and the first and second inner disks are the same as those in the conventional toroidal type continuously variable transmissions of double cavity type as shown in FIGS. 11 and 12.
In the case of the toroidal type continuously variable transmission of the present invention, since the arrangement for rotating the first and second inner disks and the sleeve synchronously is obtained by the engagement between the axial concave and convex portions, due to the engagement, a thickness of portions of the sleeve in the engagement areas between the sleeve and the first and second inner disks is not reduced. Thus, without particularly increasing the thickness of the sleeve, great torque can be transmitted while maintaining adequate endurance of the sleeve.
The other objects and features of the present invention will be apparent from the following explanation regarding embodiments thereof referring to the accompanying drawings.